1. Field of the Invention
The present invention relates to an image forming apparatus, e.g., a copying machine or printer, having a driving source for driving a sheet convey means which conveys a sheet and, more particularly, to an image forming apparatus in which a current value preset based on various kinds of sheet information and/or an image formation mode is supplied to the driving source of a sheet convey means.
2. Description of the Related Art
In an image forming apparatus, a sheet is fed out from a sheet feed tray in accordance with the image forming process. The sheet is fed again by registration rollers arranged close to an image carrier so as to be superimposed on a toner image forming on the image carrier. The toner image is transferred at a transfer region. After the toner image is fixed on the sheet by a fixing unit, the sheet is delivered outside the apparatus. Alternatively, after the toner image is fixed by the fixing unit, the sheet is reversed, and is fed out to the transfer region again so that another toner image is fixed on its second side. After the second toner image is fixed by the fixing unit, the sheet is delivered outside the apparatus.
The image forming apparatus as described above has a convey means comprised of a large number of convey roller pairs along the sheet convey path. Hence, conventionally, the convey path is appropriately divided to form a plurality of convey systems. Exclusive motors are provided for the divisional convey systems, respectively. Each motor is rotated or stopped by drive control through a controller.
Regarding the drive control of the motor, for example, the motor is controlled with a specific current pattern. Then, when the motor is to be started or reversed (rotated in the opposite direction to the forward rotation of the motor) where a large load torque is required, it is driven by a high current value. When the motor is to rotate in a steady rotation state, it is driven by a low current value. Alternatively, the motor is driven by a fixed high current value. Either method is employed.
In drive control of the motor in the image forming apparatus or the like, however, a high current value based on conditions with which the load torque increases is continuously supplied to the motor not only in starting or reversing it, but also in the steady rotation state, so that sheets having different paper qualities and sizes can be conveyed reliably. Even when a sheet which requires a small load torque and accordingly with which a low current value may suffice is to be used, an excessively high current is continuously supplied. This leads to unwanted temperature increase of the motor or a driving circuit and causes a power loss.